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# Nil Check
## Introduction
A _Nil Check_ is a type check. Failures of _Nil Check_ violate the
["tell, don't ask"](http://robots.thoughtbot.com/tell-dont-ask) principle.
Additionally to that, type checks often mask bigger problems in your source
code like not using OOP and / or polymorphism when you should.
The _Nil Check_ code smell is a case of [Simulated Polymorphism](Simulated-Polymorphism.md).
## Example
Given
```Ruby
class Klass
def nil_checker(argument)
if argument.nil?
puts "argument is nil!"
end
end
end
```
Reek would emit the following warning:
```
test.rb -- 1 warning:
[3]:Klass#nil_checker performs a nil-check. (NilCheck)
```
## Current Support in Reek
_Nil Check_ reports use of
* <code>.nil?</code> method
* <code>==</code> and <code>===</code> operators when checking vs. <code>nil</code>
* case statements that use syntax like <code>when nil</code>
* use of the safe navigation operator like `foo&.bar`
## Configuration
_Nil Check_ offers the [Basic Smell Options](Basic-Smell-Options.md).
Version data entries
27 entries across 25 versions & 2 rubygems